FIG. 1 shows a prior example of a luminance signal and color signal separating circuit. With this luminance signal and color signal separating circuit, an NTSC color video signal digitized at a sampling frequency of 4 f.sub.sc (where f.sub.sc is a subcarrier frequency) is supplied to a 1 H (one horizontal interval) delay element 11 that forms a comb filter as a vertical carrier color signal extraction filter and to a subtractor 12. The subtractor 12 subtracts a 1 H preceding video signal from the current video signal. To the output of the subtractor 12 is provided a BPF (band-pass filter) 13 that forms a horizontal carrier color signal extraction filter.
The BPF 13 has a center frequency located at a subcarrier frequency f.sub.sc (=3.58 MHz). More specifically, as shown in FIG. 2, four elements 131-134 from the input terminal IN are connected in series. The delay elements 131-134 delay the signal by 70 nsec (sampling period) as delay time T. In addition, an adder 135 is provided which adds the input signal to the input terminal IN with the output signal of the delay element 134, while a subtractor 136 is connected to the output of the delay element 132. To the subtractor 136 is supplied the output signal of the adder 135 via an inverter 137, so that the output signal of the inverter 137 is subtracted from the output signal of the delay element 132. That is, assuming that the signal level of the input terminal IN, the output signal level of the delay element 132, and the output signal level of the delay element 134 are A, B, and C, respectively, then the output level of the subtractor 136 is (B-(A+C)/2)/2, so that it is derived as a color signal. Note that the adder 135 and subtractor 136 have a capability to scale by 1/2 and output the result of their calculation.
On the other hand, the color video signal is supplied to a subtractor 15 via a delay element 14. The delay element 14 compensates for the delay caused by the BPF 13. The subtractor 15 subtracts from the output signal of the delay element 14 the output signal of the BPF 13, i.e., the color signal, and outputs the result of the subtraction as a luminance signal.
With such a prior luminance signal and color signal separating circuit, because the signal levels A, B, and C have a time difference of 140 nsec, that is, a 180.degree. phase difference, from each other, as described above, color phase information before and after horizontal color transitions are mixed during such transitions and outputted as a color signal from the subtractor 136. Thus, because a luminance signal is separated from the color video signal corresponding to the color signal whose phase information is distorted, the luminance signal and color signal are not properly separated, thus causing dot interference in color transition areas of a reproduced image.
Accordingly, it is an object of the present invention to provide a luminance signal and color signal separating circuit that can properly separate the luminance signal and color signal in horizontal color transition areas of an image, thereby minimizing dot interference in color transition areas of a reproduced image.